My guess on the psi ratings from Rolf/Co-Motion & Shimano/Santana has more to do with preventing rim dings and maintaining that super crisp road feel you get from high pressure racing tires than anything else. Even with 145psi tires we've nailed a few rims riding in pacelines; about $65 a pop for a new Velocity Deep-V rim on at least two occasions (I'm nursing a third rim that's got a marginal rim ding).

As for "why high psi", beyond the point where you have enough air your tires to give it the right shape and to prevent pinch flats, it's all about personal preferences for road feel. I like to feel every little bump and stone in the road and find it disconcerting going through fast corners on larger diameter or "cushy" tires. Right on wrong, that's my preference. When we encounter really nasty chip seal or roads with lots of expansion joints I'll yield to comfort and drop the psi down to around 115 - 120 to smooth things out.